With some practice, I am now achieving typing speeds comfortably over 200 characters per minute using the Thumb Keyboard 4. This was considerably faster than the average of 172 char/min in the initial test. I did not include the SwipeIT keyboard in the video, but the speed had stagnated at around 160-170 char/min.

SwipeIT remains the most fun to use, but the Thumb Keyboard 4 is now the fastest keyboard on Android by some distance.